Description:Columnar jointing of a Roque Nublo basanite ‘aa’ lava flow of around 4.2 million years old, overlying highly weathered Miocene basalts of around 14.2 million years.
The columnar jointing of a lava flow is formed as a lava flow cools and crystallizes into a coherent rock. As it begins to contract, shrinkage of the rock mass results in the development of numerous cracks, called joints.